PROJECTSUMMARY Cutaneous immune responses must be tightly controlled to prevent inflammatory and allergic diseases, i.e., atopic dermatitis, psoriasis, contact dermatitis, and pemphigus vulgaris. Foxp3+ regulatory T cells (T regs) play a critical role in skin immunoregulation. T regs can be naturally generatedinthethymus,orcanbeinduceddenovofromCD4+naveTcellsintheperipheryby antigen presenting cells, especially dendritic cells (DCs). The DC system is intricate and is comprised of distinct subsets such as, skin migratory Langerhans cells, skin migratory classical dermalDCsandCD103+dermalDCs,andtissueresidentDCs.Therelativeroleofeachofthese subsetsininducingTregshasbeenuntilnowindeterminate.Usinganovelapproachthatconsists of directing antigens to different subsets of DCs in vivo using monoclonal antibodies against surface receptors, we have found strong evidence that not all DCs have the ability to induce regulatoryTcells,butinsteadskinmigratoryDCexcelinthisfunction.Thisobservationleadstomy hypothesis that these subsets of skin migratory DC are intrinsically programmed by a set of transcriptional factors to induce this type of response. Additionally, local environmental/dietary factors are also described to play a role in the generation of T regs. For instance, the vitamin A active compound retinoic acid, working in conjunction with TGF?, is known to have a positive impact in the induction of T regs in the intestinal track. Similarly, there is ample evidence in vitro suggesting that Vitamin D acts on DCs and/or T cells for generation of a tolerogenic phenotype. The contribution of the proposed research is expected to be: 1) the identification of DCintrinsic signaling pathways that program subsets of skin migratory DC to the induction of T regs, 2) the determinationoftheroleofVitamins,actingonDCsand/orTcellsinvivo,forthegenerationofT regs,and3)theevaluationofthesuppressiveactivityofinducedTregsinamousemodelofatopic dermatitis.Wearepreparedtoundertaketheproposedresearchsincewehaveallthenecessary tools for studying DC functions in vivo, as well as, ample experience with DC subsets. With my mentors, I have planned the aims to achieve a comprehensive training in molecular biology approachesandmousegeneticengineeringduringtheK99phaseoftheaward.Thisprojectisof particularrelevancebecauseinmostskininflammatorydiseasesthenumberofTregsisaltered, qualitatively and/or quantitatively, suggesting their role in the pathophysiology of the illness. A detailedcomprehensionofthemechanismsofDCmediatedTreginductionwillhelptounderstand the events that lead to the appearance of skin disease. Also, this knowledge is likely to be beneficialtothedevelopmentnewtherapeutictargetstoincreaseTreg,whichinturnwillleadto improvedtreatmentofinflammatoryskindiseasesandtheircomplications.